The present invention relates to cooling equipment for use in metallurgical furnaces and more in particular to a method of manufacturing cooling plates intended for use in metallurgical furnaces and to cooling plates as such manufactured in accordance with this method.
Cooling of metallurgical furnaces is normally effected by means of cast-iron cooling plates which incorporate cast-in steel pipes for a coolant to circulate therein. Such cooling plates may be manufactured to have both straight and coiled pipes arranged in one or two rows through the thickness of the plate.
There is known a method of manufacturing cooling plates, e.g. for use in blast furnaces, according to which the steel pipes for cooling are installed in a mold and cast with molten iron (see, for example, S. M. Andonev et al., Okhlazhdenie domennykh pechei, Metallurgizdat, Moscow 1972).
The prior-art method is disadvantageous because of considerable casting stresses taking place in the body of the plate and in the cooling pipes in the course of their cooling. The casting stresses in the cooling plates are brought about with the decline in temperature because of the difference in the linear expansion coefficients of cast iron and steel, the greatest concentration of stresses occurring at the places of bending of the pipes at their exit from the body of the cooling plate. When these stresses exceed permissible level, then even local carburization of the pipes at their bendings may sharply reduce plasticity of the pipe metal with cracks tending to form therein.
When coolers are used in blast furnaces, additional thermal stresses are due to appear in the cooling plate and pipes because of abrupt alterations in thermal conditions. These additional thermal stresses are added to the stresses occurring in the course of manufacturing cooling plates, thus causing untimely damage of the latter.
There is also known a method of manufacturing cooling plates for use in metallurgical furnaces, according to which separate portions of a plate, comprising cooling pipes made from a metal with the linear expansion coefficient different from that of the plate metal, are formed (see, for example, USSR Inventor's Certificate No. 287,252; Int. cl. B22 d 19/02, published on Feb. 19, 1970).
This method is carried out by pouring the metal of the plate into a foundry mold in two stages. During the first stage, a plate is cast to have T-shaped slots, open on the rear side of the plate, formed therein. Then, as cooling pipes are fitted into these slots, the second stage of casting is performed during which molten metal, for instance, an aluminium alloy with a melting temperature of 600.degree. to 800.degree. C. and a conductivity higher than that of cast iron, is poured into the slots.
When the above method is carried out with the use of aluminium alloy, the carburization of the pipes presents no problem, but the protruded sections of the pipes undergo the same stresses as those occurring during simultaneous casting of metal into the mold provided with cooling pipes.
In addition, the use of different metals for making a cooling plate, especially when arranged in close proximity to the cooling pipes, may result in a gap between the plate portions made from different metals. This gap inhibits effective removal of heat from the furnace wall.
In general, cooling plates for metallurgical furnaces comprise a metal plate per se and cooling pipes cast therein (see, for example, a book by V. A. Sorokin, entitled "Equipment for and Operation of Blast Furnaces", Metallurgizdat Publishers, Moscow, 1944, pp.76-79).
The above-mentioned plates are disadvantageous in that they are too bulky, with temperature conditions at different sections of the plate and its support extensions being unsatisfactory to permit their effective operation. Because of considerable thermal stresses and cracks developed therein the service life of cooling plates is greatly reduced.
In addition, such plates, especially those provided with support extensions, are ineffective in use because of a great number of coolant inlet and outlet openings, to say nothing of the difficulty encountered in detecting and disconnecting the burnt-out pipes in the support extensions. Among other deficiencies is a possible penetration of moisture into the melting chamber of the furnace with the resultant impairment of operating conditions.